Defining genetic diversity of rhesus macaque Fcγ receptors with long-read RNA sequencing

Fcγ receptors (FcγRs) are membrane-bound glycoproteins that bind to the fragment crystallizable (Fc) constant regions of IgG antibodies. Interactions between IgG immune complexes and FcγRs can initiate signal transduction that mediates important components of the immune response including activation of immune cells for clearance of opsonized pathogens or infected host cells. In humans, many studies have identified associations between FcγR gene polymorphisms and risk of infection, or progression of disease, suggesting a gene-level impact on FcγR-dependent immune responses. Rhesus macaques are an important translational model for most human health interventions, yet little is known about the breadth of rhesus macaque FcγR genetic diversity. This lack of knowledge prevents evaluation of the impact of FcγR polymorphisms on outcomes of preclinical studies performed in rhesus macaques. In this study we used long-read RNA sequencing to define the genetic diversity of FcγRs in 206 Indian-origin Rhesus macaques, Macaca mulatta. We describe the frequency of single nucleotide polymorphisms, insertions, deletions, frame-shift mutations, and isoforms. We also index the identified diversity using predicted and known rhesus macaque FcγR and Fc-FcγR structures. Future studies that define the functional significance of this genetic diversity will facilitate a better understanding of the correlation between human and macaque FcγR biology that is needed for effective translation of studies with antibody-mediated outcomes performed in rhesus macaques.

Biophysical and Functional Characterization of Rhesus Macaque IgG Subclasses

Antibodies raised in Indian rhesus macaques [Macaca mulatta (MM)] in many preclinical vaccine studies are often evaluated in vitro for titer, antigen-recognition breadth, neutralization potency, and/or effector function, and in vivo for potential associations with protection. However, despite reliance on this key animal model in translation of promising candidate vaccines for evaluation in first in man studies, little is known about the properties of MM immunoglobulin G (IgG) subclasses and how they may compare to human IgG subclasses. Here, we evaluate the binding of MM IgG1, IgG2, IgG3, and IgG4 to human Fc gamma receptors (FcγR) and their ability to elicit the effector functions of human FcγR-bearing cells, and unlike in humans, find a notable absence of subclasses with dramatically silent Fc regions. Biophysical, in vitro, and in vivo characterization revealed MM IgG1 exhibited the greatest effector function activity followed by IgG2 and then IgG3/4. These findings in rhesus are in contrast with the canonical understanding that IgG1 and IgG3 dominate effector function in humans, indicating that subclass-switching profiles observed in rhesus studies may not strictly recapitulate those observed in human vaccine studies.

IgG Binding Characteristics of Rhesus Macaque FcγR

Indian rhesus macaques (Macaca mulatta) are routinely used in preclinical studies to evaluate therapeutic Abs and candidate vaccines. The efficacy of these interventions in many cases is known to rely heavily on the ability of Abs to interact with a set of Ab FcγR expressed on innate immune cells. Yet, despite their presumed functional importance, M. mulatta Ab receptors are largely uncharacterized, posing a fundamental limit to ensuring accurate interpretation and translation of results from studies in this model. In this article, we describe the binding characteristics of the most prevalent allotypic variants of M. mulatta FcγR for binding to both human and M. mulatta IgG of varying subclasses. The resulting determination of the affinity, specificity, and glycan sensitivity of these receptors promises to be useful in designing and evaluating studies of candidate vaccines and therapeutic Abs in this key animal model and exposes significant evolutionary divergence between humans and macaques.

The carbonic anhydrase inhibitor methazolamide prevents amyloid beta-induced mitochondrial dysfunction and caspase activation protecting neuronal and glial cells in vitro and in the mouse brain

Mitochondrial dysfunction has been recognized as an early event in Alzheimer's disease (AD) pathology, preceding and inducing neurodegeneration and memory loss. The presence of cytochrome c (CytC) released from the mitochondria into the cytoplasm is often detected after acute or chronic neurodegenerative insults, including AD. The carbonic anhydrase inhibitor (CAI) methazolamide (MTZ) was identified among a library of drugs as an inhibitor of CytC release and proved to be neuroprotective in Huntington's disease and stroke models. Here, using neuronal and glial cell cultures, in addition to an acute model of amyloid beta (Aβ) toxicity, which replicates by intra-hippocampal injection the consequences of interstitial and cellular accumulation of Aβ, we analyzed the effects of MTZ on neuronal and glial degeneration induced by the Alzheimer's amyloid. MTZ prevented DNA fragmentation, CytC release and activation of caspase 9 and caspase 3 induced by Aβ in neuronal and glial cells in culture through the inhibition of mitochondrial hydrogen peroxide production. Moreover, intraperitoneal administration of MTZ prevented neurodegeneration induced by intra-hippocampal Aβ injection in the mouse brain and was effective at reducing caspase 3 activation in neurons and microglia in the area surrounding the injection site. Our results, delineating the molecular mechanism of action of MTZ against Aβ-mediated mitochondrial dysfunction and caspase activation, and demonstrating its efficiency in a model of acute amyloid-mediated toxicity, provide the first combined in vitro and in vivo evidence supporting the potential of a new therapy employing FDA-approved CAIs in AD.

Human Non-neutralizing HIV-1 Envelope Monoclonal Antibodies Limit the Number of Founder Viruses during SHIV Mucosal Infection in Rhesus Macaques

HIV-1 mucosal transmission begins with virus or virus-infected cells moving through mucus across mucosal epithelium to infect CD4+ T cells. Although broadly neutralizing antibodies (bnAbs) are the type of HIV-1 antibodies that are most likely protective, they are not induced with current vaccine candidates. In contrast, antibodies that do not neutralize primary HIV-1 strains in the TZM-bl infection assay are readily induced by current vaccine candidates and have also been implicated as secondary correlates of decreased HIV-1 risk in the RV144 vaccine efficacy trial. Here, we have studied the capacity of anti-Env monoclonal antibodies (mAbs) against either the immunodominant region of gp41 (7B2 IgG1), the first constant region of gp120 (A32 IgG1), or the third variable loop (V3) of gp120 (CH22 IgG1) to modulate in vivo rectal mucosal transmission of a high-dose simian-human immunodeficiency virus (SHIV-BaL) in rhesus macaques. 7B2 IgG1 or A32 IgG1, each containing mutations to enhance Fc function, was administered passively to rhesus macaques but afforded no protection against productive clinical infection while the positive control antibody CH22 IgG1 prevented infection in 4 of 6 animals. Enumeration of transmitted/founder (T/F) viruses revealed that passive infusion of each of the three antibodies significantly reduced the number of T/F genomes. Thus, some antibodies that bind HIV-1 Env but fail to neutralize virus in traditional neutralization assays may limit the number of T/F viruses involved in transmission without leading to enhancement of viral infection. For one of these mAbs, gp41 mAb 7B2, we provide the first co-crystal structure in complex with a common cyclical loop motif demonstrated to be critical for infection by other retroviruses.

Role of ADAMs in the ectodomain shedding and conformational conversion of the prion protein

The cellular prion protein (PrP^C) is essential for the pathogenesis and transmission of prion diseases. PrP^C is bound to the plasma membrane via a glycosylphosphatidylinositol anchor, although a secreted, soluble form has also been identified. Previously we reported that PrP^C is subject to ectodomain shedding from the membrane by zinc metalloproteinases with a similar inhibition profile to those involved in shedding the amyloid precursor protein. Here we have used gain-of-function (overexpression) and loss-of-function (small interfering RNA knockdown) experiments in cells to identify the ADAMs (adisintegrin and metalloproteinases) involved in the ectodomain shedding of PrP^C. These experiments revealed that ADAM9 and ADAM10, but not ADAM17, are involved in the shedding of PrP^C and that ADAM9 exerts its effect on PrP^C shedding via ADAM10. Using dominant negative, catalytically inactive mutants, we show that the catalytic activity of ADAM9 is required for its effect on ADAM10. Mass spectrometric analysis revealed that ADAM10, but not ADAM9, cleaved PrP between Gly²²⁸ and Arg²²⁹, three residues away from the site of glycosylphosphatidylinositol anchor attachment. The shedding of another membrane protein, the amyloid precursor protein β-secretase BACE1, by ADAM9 is also mediated via ADAM10. Furthermore, we show that pharmacological inhibition of PrP^C shedding or activation of both PrP^C and PrP^Sc shedding by ADAM10 overexpression in scrapie-infected neuroblastoma N2a cells does not alter the formation of proteinase K-resistant PrP^Sc. Collectively, these data indicate that although PrP^C can be shed through the action of ADAM family members, modulation of PrP^C or PrP^Sc ectodomain shedding does not regulate prion conversion.

Crystal structure of the TetR/CamR family repressor Mycobacterium tuberculosis EthR implicated in ethionamide resistance

Ethionamide has been used for more than 30 years as a second-line chemotherapeutic to treat tuberculosis patients who have developed resistance to first-line drugs, such as isoniazid (INH) and rifampicin. Activation of the pro-drug ethionamide is regulated by the Baeyer-Villiger monooxygenase EthA and the TetR/CamR family repressor EthR, whose open reading frames are separated by 75 bp on the Mycobacterium tuberculosis genome. EthR has been shown to repress transcription of the activator gene ethA by binding to this intergenic region, thus contributing to ethionamide resistance. We have determined the crystal structure of EthR, to 1.7A resolution, revealing a dimeric two-domain molecule with an overall architecture typical for TetR/CamR repressor proteins. A 20A long hydrophobic tunnel-like cavity in the "drug-binding" domain of EthR is occupied by two 1,4-dioxane molecules, a component of the crystallisation buffer. Comparing the present structure to those of the homologues Staphylococcus aureus QacR and Escherichia coli TetR leads to the hypothesis that the hydrophobic cavity constitutes a binding site for an as yet unknown ligand that might regulate DNA-binding of EthR.